PURPOSE: To facilitate shaking-out of sand for a casting and to improve the workability by forming a collapsible mold with molding sand containing grains composing of β-2CaO.SiO2 as at least a part of the component.

CONSTITUTION: The collapsible mold is formed by using the molding sand (about 10μW2mm average grain size) containing the grain composing of β-2CaO.SiO2 as at least a part of the component (≥about 10wt.% containing quantity). At the time of executing the cast by using the mold, the β-2CaO.SiO2 becomes α-2CaO.SiO2 by pouring molten metal and further becomes γ-2CaO.SiO2 by slow-cooling this and the volume is increased by dislocation into γ to become about 20μ grain size and the mold is collapsed. By this method, the cast for the casting having complicated shape or slender hollow part and the shaking-out of the sand are facilitated.